Multiple versions

If you want to run multiple versions on the same system (e.g. 1.9.3 and 1.8.7), the easiest way is to use RVM or rbenv.

RubyGems

gem is the package manager of sorts for Ruby modules (called Gems), somewhat comparable to what pacman is to Arch Linux. The gem command will be installed if you followed the installation instructions above.

Running as normal user

When running gem as a user, the gems will be installed into ~/.gem and not affect anyone else, although it might be worth noting that not all gems are happy with being installed in this way, and might insist on being installed by root (especially if they have native extensions). This is considered the best way to manage gems on Arch.

To use gems which install binaries, you need to add ~/.gem/ruby/2.0.0/bin to your $PATH.

This per-user behavior is enabled via /etc/gemrc and can be overridden by a ~/.gemrc file.

Running as root

When running as root, the gems will be installed into /root/.gems and will not be installed to /usr/lib/ruby/gems/.

Bundler solves these problems to some extent by packaging gems into your application. See the section below on using bundler.

Updating RubyGems

$ gem update

Installing a gem

This example installs the MySQL ruby gem:

$ gem install mysql

The process can be sped up somewhat if you do not need local documentation:

$ gem install mysql --no-rdoc --no-ri

The gem will now be downloaded, compiled if necessary, and installed.

Bundler

Bundler installs gems (including those with native extensions) directly into your application, which works very well for shared hosting and easy deployment of Ruby on Rails applications for example. Bundler also resolves dependencies as a whole, rather than individually like RubyGems, making things a lot easier. To install:

$ gem install bundler

Bundler seems to want to install gems system-wide, contrary to the current default behaviour of gem itself on Arch. To correct this, add the following line to your ~/.bashrc:

export GEM_HOME=~/.gem/ruby/2.0.0

To start a new bundle:

$ bundle init

Then add your required gems into "Gemfile" in the current directory (created by bundle init):

Gemfile

gem "rails", "3.2.9"
gem "mysql"

Finally, run the following to install your gems:

$ bundle install

Or, alternatively, in order to install locally to .bundle under the working directory:

$ bundle install --path .bundle

Managing RubyGems using pacman

Instead of using the gem command directly you can use pacman to manage the installed gems like normal packages. There are a lot of ruby packages available from AUR. Ruby packages follow the naming convention ruby-[gemname]. As an alternative you can use the tool pacgemAUR which automatically creates arch packages from gems and installs them afterwards using pacman.

Warning: Many ruby gem packages in the AUR explicitly use the --no-user-install or --user-install command line switches, bypassing the global setting found in /etc/gemrc or the users own ~/.gemrc. You're editing the PKGBUILD file before you install, right?